Try to make a convincing invitation to drive registration. Don't give them a reason to feel like your invitation is a corporate "fill in the blank" form. Target a specific segment and make a personal connection, so you can retain them longer.
If you have a company blog, it can be the best place to announce your webinar. Through blogs, you can target your audience by discussing how to register for the webinar and the webinar content itself.
An on-demand presentation is a pre-recorded webinar which can be viewed by your audience any time they'd like. Unlike webinars, on-demand presentations do not require a large number of internal links.